1. Field of the Invention
The subject invention relates generally to image displays, and more particularly to apparatus for automatically correcting misconvergence and amplitude errors of color images generated by CRTs in a color display projector.
2. Description of the Prior Art
In the prior art, convergence correction of CRT images generated in color projectors has been laboriously approximated manually prior to use of the projector. Such convergence correction requires skilled personnel to adjust a large number of potentiometers, which often interact. During this time consuming manual convergence process, position drift caused by electronic or mechanical component temperature changes often occurs, making accurate convergence over the entire image area very difficult. Spatial gray scale correction has also been done manually and is similarly time consuming and difficult.
Another prior art approach to convergence adjustment utilizes light sensors built into the projection screen along the edges of the intended display. This approach has the advantage of automatic control, however, only size and centering of the image are controlled. The approach is limited to fixed installations, i.e., those where the projector apparatus is in fixed relation with the display screen, such as in a standard television set. It is further not adaptable to aspect ratio or size differences required when different video sources are used, and does not provide linearity corrections needed for convergence inside the display boundary.
The foregoing prior art approaches also do not address the problem of misconvergence caused by electronic and mechanical drift during operation of the projector. Such drift inevitably results from temperature changes and vibration during operation of conventional display projectors.